Those of our investigations which involve controlled dietary restriction have now arrived at the stage where we are able to obtain a striking prolongation of the lifespan of an already long-lived strain of mouse. This prolongation is accompanied by a relative preservation into advanced age of immune response capacity. In our recentest work we find that immune rejuvenation and probably lifespan extension can be achieved by gradual dietary restriction beginning at mid-adulthood. This is unlike most or all prior work, which has only been done with restriction at time of weaning. In the future we shall be emphasizing mid-life restriction and it's effect upon immune, lifespan, and disease parameters. Effects of dietary restriction upon psychological tests, and chromatin will also be assessed.